The present invention relates to an apparatus for the continuous production of oriented hollow bodies from a thermoplastic and which provides very high productivity.
It is known to produce hollow bodies having improved mechanical properties from a thermoplastic, by effecting the expansion and final shaping of preforms which are at a temperature which induces a molecular orientation. In general, the preforms are employed at a temperature below the crystalline melting point of the thermoplastic of which they are made.
Numerous techniques have been developed for the industrial-scale production of oriented hollow bodies from thermoplastics. One of the most attractive techniques comprises producing preforms by blowing a portion of a tubular parison in a preform mold, bringing these preforms to a suitable temperature for their orientation and then introducing them into molds in which the final molding by blowing is carried out.
An apparatus which exploits this technique is described in U.S. Pat. No. 3,767,747 assigned to Owens Illinois Glass Co.
This apparatus comprises two molding units, each comprising a preform mold and a final blowing mold, located on either side of an extrusion installation which delivers a tubular parison. Each unit executes a reciprocating movement so as to present its preform mold under the extrusion head and then under blowing nozzles, also located on either side of the extrusion installation.
However, taking into account the sequenced movement of the molding units, the necessarily limited number of molds and the need to keep each preform in its preform mold for a sufficient period to permit its thermal conditioning, this type of apparatus only achieves low production.